This invention relates to nitrile barrier resin latex coatings which contain a thickener comprising polyvinyl pyrrolidone. These coatings are an improvement over the coatings described in U.S. Ser. No. 135,383, which is herein incorporated by reference.
Many varieties of coating compositions have been used in the past based on various polymeric materials. These coatings are either solvent-type or aqueous-type. The solvent-type coatings are disadvantageous in that large amounts of volatile organic solvents are present. These solvents are costly and hazardous. The aqueous-type coatings, especially nitrile barrier resin coatings, are also disadvantageous in that they generally are not continuous and often have been found to contain pin holes, voids and the like.
The aqueous dispersion coatings of this invention avoid the disadvantages of the solvent-type coating composition by the use of water as the predominating component of the solution. Moreover, the problems normally associated with latex coatings have been solved by the addition of a particular class of thickening agents which are more fully described below. These coatings also have good chemical resistance and are excellent oxygen barriers.
The thickening agents are also advantageous in that they reduce sagging so that the coating will not run off the substrate. Finally, these thickening agents exhibit thixotropy so that when shear is applied to the latex over a period of time, the apparent viscosity decreases. The viscosity returns to its original value when the shear is removed. This thixotropic behavior is evidence of an interaction between latex particles and thickener molecules.